1. Field of the Invention
The present invention relates to a high vacuum valve which is to be used in order to depressurize a vacuum chamber for chemical reaction in a physical or chemical machine or the like, and which is to be used in other fields.
2. Description of the Related Art
For example, in a manufacturing apparatus for producing a semiconductor, a chemical treatment such as etching is performed in a vacuum chamber. At this time, a vacuum pump is used in order to depressurize the vacuum chamber and a high vacuum valve is used for closing and opening an external flow-channel which interconnects the vacuum pump and the vacuum chamber.
As shown, for example, in FIG. 2, the high vacuum valve generally comprises a housing 40 having an axially extending valve flow channel 41, two ports 42, 43 connected to openings 42a, 43a respectively formed in one end and side surface of the valve flow channel 41, and respectively connected to the vacuum pump and the vacuum chamber, a valve seat 44 provided around the opening of the one end of the valve flow channel 41, a valve member 45 for opening and closing the valve seat 44, a piston 46 for causing the valve member 45 to perform opening/closing operations, a valve shaft 47 interconnecting the piston 46 and the valve member 45, and a flexible metal-bellows 48 housed in the valve flow channel 41 and hermetically surrounding a periphery of a substantially total length of the valve shaft 47 (Japanese Patent Application Laid-Open No. 9-133238).
In the conventional high-vacuum valve constructed as discussed above, a molded bellows is employed as the metal bellows. The molded bellows is made by pressure-molding a cylindrical metal material to thereby cause concave regions and convex regions to be alternately formed along an axial direction of the cylindrical metal material. The molded bellows can be mass-produced by a few manufacturing processes, so that the molded bellows has the advantage that the manufacturing cost of the molded bellows can be restricted so as to be low. However, on the other hand, the molded bellows is poor in flexibility and bending property.
Incidentally, when in order to improve depressurization characteristic of the vacuum chamber, the capacity of the vacuum pump is improved and the flow rate of fluid passing through the vacuum valve is increased, high fluid-pressure is applied to the metal bellows provided in the valve flow channel. At this time, the fluid pressure is applied to the metal bellows as a force to be exerted in a bending direction. When such a force in the bending direction is repeatedly applied to the metal bellows, crack or the like is easy to be produced in the bellows by metal fatigue which is brought about by repeated bent-deformation of the bellows, so that there is a possibility that a life of the product will be reduced. This is noticeable particularly in the case of the molded bellows having the poor bending property as discussed above. When consideration is given to durability and manufacturing cost, it is desirable that a length of the metal bellows is rather short.
However, in the conventional high vacuum valve, if the length of the metal bellows is reduced in preference to durability, a sufficient stroke amount of the valve shaft, namely, a sufficient increase in valve-member opening can not be ensured, since the molded bellows is poor in flexibility as discussed above. Consequently, there is a problem that a sufficient flow rate of fluid allowed to flow by the valve can not be ensured.